This application is related to Application (EH-10151) filed on Jun. 12, 1998 entitled xe2x80x9cThermal Barrier Coating System Using Localized Bond Coat and Article Having the Samexe2x80x9d.
The present invention provides the practical production ready process for cleaning superalloy components prior to the application of a ceramic thermal barrier coating. The ceramic thermal barrier coating towards which the invention process is directed is the type of coating described in the U.S. Pat. No. 5,262,245.
From a historical perspective, superalloys were originally used in the uncoated condition in gas turbine engines; in those early engines, the operating temperatures were sufficiently low that surface oxidation was not a problem. As operating temperatures increased and stronger alloys were developed (these stronger alloys tended to be more susceptible to oxidation and corrosion) various coatings were developed to protect the superalloy materials from oxidation and corrosion, and these types of coatings continue to be used in the present time. With yet further temperature increases, it became necessary to provide thermal barrier or insulation coatings on certain gas turbine components. Initially and these coatings were adhered to the existing metallic coatings. See for example U.S. Pat. No. 4,585,481 for a general description of oxidation protective coatings and see U.S. Pat. No. 4,321,311 and 5,514,482 for a background on the state-of-the-art electron beam physical vapor deposited (EBPVD) thermal barrier coatings (TBC).
The existing thermal barrier coatings with bond coats have been highly successful, but new engine designs which incorporate higher rotational speeds have resulted in a requirement to reduce the weight of the thermal barrier coating without sacrificing thermal insulations. In rotating blades, the mass of the coating provides a substantial pull on the blade root and by reducing the mass of the coating higher rotational speeds can be achieved thereby increasing engine efficiency and potentially allowing a reduction number of parts in the engine.
U.S. Pat. No. 5,262,245 describes a bond coat free thermal barrier coatings.
The problem with a bond coat free coating is to insure that the EBPVD ceramic coating adheres to the superalloy substrate.
This invention relates to the field of metal surface cleaning.
This invention also relates to the field of Electron Beam Physical Vapor Deposited Ceramic Coatings. More specifically this invention relates to a method for cleaning superalloy surfaces so that a subsequently deposited EBPVD ceramic coating will be durable and adherent.